显式创建类型不符合目标类型

Question

我真的不理解，因为在我看来类型一致性的基础知识。我在Creation instruction lists explicit creation type which does not conform to type of target上有一个create {JANITZA_DEVICE} l_device.make_from_file_path (a_file_path)的埃菲尔Studio 19.5企业版。

SMA_INVERTER_MANAGER_CSV

class
    SMA_INVERTER_MANAGER_CSV

inherit
    SUNSPEC_DEVICE_CSV[SMA_INVERTER_MANAGER_DEVICE]

create
    make

SUNSPEC_DEVICE_CSV

deferred class
    SUNSPEC_DEVICE_CSV[G -> SUNSPEC_DEVICE create make_from_file_path end]

inherit
    CONSUMPTION_SECTOR_CSV[G]
        redefine
            process_file,
            set_header_csv
        end

feature --

    process_file (a_file_path: PATH)
        require else
            attached a_file_path.entry
            attached consumption_sector
        local
            l_device: like devices.item
        do
            check
                attached_consumption_sector: attached consumption_sector
            then
                if is_valid_file_path (a_file_path) then
                    if attached a_file_path.utf_8_name.has_substring ("janitza_UMG604") then
                        create {JANITZA_DEVICE} l_device.make_from_file_path (a_file_path) -- The compiler doesn't agree!
                    else
                        create l_device.make_from_file_path (a_file_path)
                    end
                    l_device.load_measuring_point (create_measuring_points, measuring_point_db_service, consumption_sector)
                    devices.extend (l_device)
                    Precursor (a_file_path) -- load measure_units from csv_row
                    devices.wipe_out
                end
            end
        ensure then
            devices.is_empty
        end

CONSUMPTION_SECTOR_CSV [G]

deferred class
    CONSUMPTION_SECTOR_CSV[G -> MEASURING_POINT_DEVICE]

feature -- Access

    devices: LINKED_SET[G]

SUNSPEC_DEVICE

class
    SUNSPEC_DEVICE

inherit
    MEASURING_POINT_DEVICE
        redefine
            default_create,
            set_measuring_point,
            out
        select
            serial
        end

    MODBUS_DEVICE
        rename
            serial as modbus_serial,
            set_serial as set_modbus_serial
        undefine
            make
        redefine
            default_create,
            make_from_file_path,
            name_from_file_path,
            out
        select
            set_modbus_serial
        end

create
    make_from_file_path

JANITZA_DEVICE

class
    JANITZA_DEVICE

inherit
    SUNSPEC_DEVICE
        redefine
            set_measure_units,
            name_from_file_path
        end

create
    make_from_file_path

Answer 1

这是一个简化的情况：

class ANIMAL

class CAT inherit ANIMAL

class HOUSE_CAT inherit CAT

class DOG inherit ANIMAL

class
    ENCLOSURE [G -> ANIMAL]
feature
    specimens: LIST [G] --> The actual type will vary with the generic parameter

    describe
        do
            print(specimens.generating_type)
        end

class
    APPLICATION

feature

    test
        local
            l_cat: CAT
            l_animal_enclosure: ENCLOSURE [ANIMAL]
            l_cat_enclosure: ENCLOSURE [CAT]
            l_house_cat_enclosure: ENCLOSURE [HOUSE_CAT]
            l_dog_enclosure: ENCLOSURE [DOG]
        do
            create l_specimen

            create l_animal_enclosure
            l_animal_enclosure.describe --> LIST [ANIMAL]
            l_animal_enclosure.specimens.add (l_cat) --> Fine, CAT conforms to ANIMAL

            create l_cat_enclosure
            l_cat_enclosure.describe --> LIST [CAT]
            l_cat_enclosure.specimens.add (l_cat) --> Fine, CAT conforms to CAT

            create l_house_cat_enclosure
            l_house_cat_enclosure.describe --> LIST [HOUSE_CAT]
            l_house_cat_enclosure.specimens.add (l_cat) --> ERROR, CAT does not conform to HOUSE_CAT


            create l_dog_enclosure
            l_dog_enclosure.describe --> LIST [DOG]
            l_dog_enclosure.specimens.add (l_cat) --> ERROR, CAT does not conform to CAT
        end

在您的情况下，devices: LINKED_SET [G]太模糊了，没有任何证据表明JANITZA_DEVICE是有效的类型，因为G可能最终会降低层次结构（例如HOUSE_CAT- > CAT；您不能将CAT替换为HOUSE_CAT，因此HOUSE_CAT的列表不能容纳CAT）或在层次结构的单独分支中（例如DOG-> ANIMAL；狗不是猫，它们只有一个共同的祖先。）

如果将{ENCLOSURE}.specimens声明为LIST [ANIMAL]而不是LIST [G]，则无论实际的通用参数如何，describe都将始终打印LIST [ANIMAL]，因为类型不会改变，因此先前的代码可以编译并正常运行。 同样，如果将{CONSUMPTION_SECTOR_CSV}.devices声明为LINKED_SET [SUNSPEC_DEVICE]而不是LINKED_SET [G]，则无论SUNSPEC_DEVICE的实际类型如何，它都可以容纳G的所有后代。

或者，您可以将JANITZA_DEVICE的特定部分从CONSUMPTION_SECTOR_CSV移到CONSUMPTION_SECTOR_CSV的后代，G处于封闭状态，如

class
    JANITZA_CONSUMPTION_SECTOR_CSV -- No generic here!
inherit
    CONSUMPTION_SECTOR_CSV [JANITZA_DEVICE]
        redefine
            process_file -- Add the parts specific to `JANITZA_DEVICE` in the implementation
        end

这将确保devices可以容纳实例JANITZA_DEVICE。

Answer 2

我认为user10481525已经解释了错误的原因。您的代码不能保证JANITZA_DEVICE的所有潜在后代中的G都符合SUNSPEC_DEVICE_CSV。

您已声明属性devices: LINKED_SET [G]。因此，局部变量l_device: like devices.item的类型为G。在JANITZA_DEVICE的后代中附加SUNSPEC_DEVICE_CSV可能无效。为什么？因为G可以是SUNSPEC_DEVICE的任何后代。

例如，假设您有一个后代class FOO_DEVICE_CSV inherit SUNSPEC_DEVICE_CSV [FOO_DEVICE]； class FOO_DEVICE inherit SUNSPEC_DEVICE。您的本地变量将有效地解析为local l_device: FOO_DEVICE。因此，后代将尝试将类型为JANITZA_DEVICE的对象附加到该对象。但这是无效的，因为JANITZA_DEVICE不符合FOO_DEVICE：

feature devices: LINKED_SET [FOO_DEVICE] ... local l_device: FOO_DEVICE ... create {JANITZA_DEVICE} l_device.make_from_file_path (a_file_path) -- Invalid!